In the foundational defining work for 'Grounded Theory', so called because the developed theory is explicitly grounded in the data, Glaser and Strauss explain why 'discovery' is so important:

Whether or not there is a previous speculative theory, discovery gives us a theory that "fits or works" in a substantive of formal area (though further testing, clarification or reformulation is still necessary), since the theory has been derived from dat, not deduced from logical assumptions.

It is real; it is tangible; and - most importantly, it works because it comes from the data set.